344 THE CAMBRIAN. [bull. 81. 



compact gray sandstone occurs, lying in nearly horizontal beds. Lower 

 down they dip 3° to 5° to the northeast. This dip increases to 7° to 

 8° at the iron bridge. Following across the strike down the stream to 

 where the beds are horizontal, above the entrance to the Chasm, the 

 measured section shows 333 feet in thickness from near the granite to 

 the highest beds observed. 



The section as measured from the mouth of the Au Sable Chasm to 

 the summit beds above the fault is as follows: 



SECTION. 



Feet. 



(1) Compact, fine-grained, steel-gray, buff, and light gray sandstone, in layers 



from 6 inches to 5 feet in thickness (20 layers) 45 



Strike N. 30° E. Dip. 5° E. 



(2) Massive layers, light gray, fiue-grained sandstone, very hard, breaking up 



into thin layers, •£ to 3 inches thick 6 



(3) Compact, gray sandstone in three layers; 1 foot 5 inches, 1 foot 6 inches, 2 



feet 1 iuch 5 



(4) Light gray and buff sandstone, three layers 4 *6 



(5) Light gray compact sandstone, with Lingulepis acuminata, Conrad 1 



Strike N 30° E. Dip 5° E., at foot of rapids. 



(6) Light gray, fine-grained, compact sandstone, in layers varying from 6 



inches to 18 inches in thickness 6 



(7) Of the same general character as 6, in massive layers, breaking up into thin 



layers on exposure. Occasional layers contain many small, fiat concre- 

 tions of clay shale and also fragments of Lingulepis. At 34 feet from 

 the base Uyolithes primordialis f and Lingulepis acuminata occur near the 

 boat-lauding in the Chasm. Thirty-five feet higher up in the same light 

 gray compact sandstone L. antiqua occurs in association with Ptychoparia 

 minuta 117 



At this line a fault breaks the section with a down -throw to the north- 

 east. The river and Chasm follow the fault from the Elbow to the 

 Devil's Oven, where the section is taken up again. 



(1) Massive layers of light gray, hard, compact sandstone. Prof R. P. Whitfield 



found at this horizon Palwacmcea typica, Ptychoparia minuta 30 



(2) Evenly bedded gray, buff, and yellowish sandstone, hard, compact and in 



layers 1 to 4 feet in thickness 165 



(3) Thinner bedded gray and buff sandstone, with Protichnites tracks above the 



mill-dam and above the bridge at Birmingham 45 



Strike NE. ; dip 5° SE. 



Ripple marks are very numerous and Lingulepis acuminata is abundant 15 feet 

 above the Protichnites be<L and extends about 25 feet to the top of the section. 

 Some of the layers are a little calcareous and full of annelid trails and borings. 



Estimating the amount of repetition of strata in the two sections 

 there remains a lower series of 210 feet, and an upper of 140 feet, or a 

 total thickness of 350 feet with the summit and base of the formation 

 unseen. 



Section at Whitehall. — There is a fine section exposed at Whitehall. 

 Kew York, that serves to correlate the sections of Chateaugay and 

 Au Sable Chasm. At the former the upper fauna is present and at 

 Au Sable Chasm the Ptychoparia minuta subfauna. At Whitehall the 



